Caliper Question

[Dave Nereson]

----- Original Message ----- 
From: "Alan" <tune4u@earthlink.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Tuesday, September 02, 2003 6:45 PM
Subject: Qaliper Question


> I don't own a micrometer. Maybe I should. 
> But my trusty caliper measures tuning pins, center pins, etc., very
> nicely. 
> It's strings that give me trouble. I can measure the same string several
> times and get 2-3 thousands differences in the readings. I think it has
> to do with getting the wire exactly knowing perpendicular to the jaws
> and then knowing how much to "squeeze" with the thumb roller ... 
> Anyone out there mastered the art of measuring strings with calipers?
> Alan R. Barnard
> Salem, MO

    Strings don't always measure exactly the same diameter along their whole length.  They can stretch more in certain areas, thus thinning their diameter, especially in older pianos, but usually not more than a thousandth or so.
    Center pins, tuning pins, bridge pins -- they can all vary in diameter a bit.  I never get consistent readings in a batch that are exactly the same -- there's always a variance of about a mil (a thousandth) whether using calipers or a micrometer.  
    With the calipers, y'always gotta check your calibration first (make sure zero is zero), wheareas the micrometer seems to stay calibrated better.  I trust the micrometer just a little more than the calipers.  If the calipers have two beveled edges at the end of the prongs that meet like a wire cutter, then if you're holding the thing being measured, or the caliper, at an angle, you can get a false reading.  So it's better to have the pin or string between the two flat faces.
    I find that for piano wire, the circular wire gauge works just as well:  if the string "just goes" through the slot, that's what size it is;  if it goes through real easy, but not through the next smaller size, then it's the half-size in between.  
    Talkin'  'merican here . . . if the wire might be metric, double check with the mic or calipers.
    --David Nereson, RPT